The present invention relates to document publication in a publish and subscribe document distribution data processing system and more particularly to durable subscription management for a publish and subscribe document distribution data processing system.
Content distribution in the context of computing refers to the electronic distribution of content across a computer communications network. Traditional modes of distributing content require the indexing of available content in a form addressable by an end user to retrieve the content from over the network. The most popular mechanism for distributing content, of course, is the World Wide Web, hereinafter the “Web”. Other mechanisms are favored for content distribution, as well, most notably, through the use of electronic messaging such as e-mail. In fact, mass distribution of promotional content often relies upon bulk e-mail rather than the passive posting of content on Web pages disposed about the Web. Venerable forms of content distribution also include discussion forums and shared document libraries providing hierarchically arranged threads of discussions.
Given the vast volume of content available and of interest to individuals globally, aggregation technologies have evolved to provide the end user with the ability to subscribe to content of interest so as to have the content of interest pushed to the subscribing end user without requiring the end user to manually located and pull content of interest. The publish and subscribe paradigm, though effective, can become an overwhelmingly difficult management problem in that a large volume of content is continuously automatically delivered to the subscriber as the content becomes available. With the passage of enough time, the subscriber can become swamped with unviewed content and must filter the unviewed content to truly identify content of temporal relevance. Indeed, with enough passage of time, the process of sifting through delivered content under subscription can approach the inefficiency corresponding to the manual pulling of the content from the source of the content in the absence of the subscription.
To address the challenge of out-of-control delivery of subscribed content, durable subscriptions have become a popular mechanism used by content subscribers. In a durable subscription, content continues to be collected for a subscriber of the content during periods of inactivity of the subscriber such that when the subscriber becomes active, the content received during the period of inactivity remains accessible to the subscriber. In a durable subscription, however, only a maximum volume of content is permitted pending during a period of inactivity by the subscriber pending a review by the subscriber. Once the maximum volume has been reached for a subscribed topic of interest, subsequent content once published is ignored. Consequently, once the subscriber becomes active, the subscriber will not necessarily review the most temporally relevant content for a durably subscribed topic.
Other solutions exist to address the deficiency of durable subscriptions. Examples include the retained publications algorithm in which only the most recent content for a topic will be viewed by a subscriber once active. However, the retained publications algorithm does not permit the recently active subscriber to view any historical context of content posted for a subscribed topic. Yet other solutions include shared circular queues of content that store a fixed number of most recently published content for a subscribed topic for all viewers. Yet, in a shared circular queue, the removal or deletion of content by one subscribing viewer prevents other subscribing viewers from continuing to access the removed or deleted content.